Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta Ga., Time-Warner Cable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass., and others, provide cable television services to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial (“HFC”) cable system which have data rates of about 10 Mega-bits-per-second (“Mbps”) to 30+ Mbps.
The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that requires a large bandwidth for downloading and viewing. Most Internet Service Providers (“ISPs”) allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network (“PSTN”) at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps to 30+Mbps available on a coaxial cable or HFC cable system on a cable television network.
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., Motorola Corporation of Arlington Heights, Ill., Cisco Corporation of San Jose, Calif., Scientific-Atlanta, of Norcross, Ga. and others offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks (“LANs”) and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a data rate of up to 30+Mbps, which is a much larger data rate than can be supported by a modem used over a serial telephone line.
Many cable television networks provide bi-directional cable systems, in which data is sent “downstream”, from a “headend” to a customer, as well as “upstream”, from the customer back to the headend. The cable system headend is a central location in the cable television network and, further, is responsible for sending cable signals in the downstream direction and receiving cable signals in the upstream direction. An exemplary data-over-cable system with RF return typically includes customer premises equipment such a customer computer, a cable modem, a cable modem termination system, a cable television network, and a data network such as the Internet.
Some cable television networks provide only uni-directional cable systems, supporting only a “downstream” data path, which provides a path for flow of data from a cable system headend to a customer. A return data path via a telephone network, such as a public switched telephone network provided by AT&T and others, (i.e., a “telephone return”) is typically used for an “upstream” data path, which provides a path for a flow of data from the customer back to the cable system headend. A cable television system with an upstream connection to a telephone network is typically called a “data-over-cable system with telephone return.”
An exemplary data-over-cable system with a telephone return typically includes customer premises equipment (“CPE”) entities (such as a customer computer or a Voice over Internet Protocol (“VoIP”) device), a cable modem, a cable modem termination system, a cable television network, a public switched telephone network, a telephone remote access concentrator, and a data network (e.g., the Internet). The cable modem termination system and the telephone remote access concentrator combined are called a telephone return termination system.
If the customer premises equipment entity comprises a telephone or a device capable of sending and receiving video or voice signals, the cable modem has to be capable of sending and receiving such signals. In such cases the cable modem typically comprises an internal media terminal adapter, which provides a network interface functionality that accepts analog voice inputs or video signal and generates IP packets using the Real Time Transport protocol, for instance.
In a bi-directional cable system, when the cable modem termination system receives data packets from the data network, the cable modem termination system transmits received data packets downstream via the cable television network to a cable modem attached to the customer premises equipment entity. The customer premises equipment entity sends response data packets to the cable modem, which sends the response data packets upstream via the cable network. The cable modem termination system sends the response data packets back to the appropriate host on the data network.
In the case of a telephone return system, when a cable modem termination system receives data packets from the data network, the cable modem termination system transmits the received data packets downstream via the cable television network to a cable modem attached to a customer premises equipment entity. The customer premises equipment entity sends response data packets to the cable modem, which sends response data packets upstream via the public switched telephone network to a telephone remote access concentrator. Next, the telephone remote access concentrator sends the response data packets back to the appropriate host on the data network.
When a cable modem used in the cable system with the telephone return is initialized, a connection is made to both the cable modem termination system via the cable network and to the telephone return termination system via the public switched telephone network. As the cable modem is initialized, the cable modem initializes one or more downstream channels via the cable network. Also upon initialization, the cable modem receives a configuration file from a configuration server via a trivial file-transfer protocol (“TFTP”) exchange.
Every host or a router on the Internet has an Internet Protocol (“IP”) address, which encodes its network address and a host number to form a unique network address combination. All hosts on the same network must have the same network number, and this property of Internet Protocol addressing has been causing some problems as the size of networks is constantly growing. As the number of distinct local area networks (“LANs”) grows, managing those networks can be problematic since each local area network would need a separate network number that, consequently, has to be announced worldwide. Furthermore, moving a network device from one local area network to another requires the network device to change its Internet Protocol address, which in turn may mean modifying its configuration files and announcing a new Internet Protocol address to the world. If some other network device is given the newly released Internet Protocol address, that network device will get data intended for the original network device until the Internet Protocol address has propagated all over the world.
One of the currently existing solutions allows a network to be split into several parts for an internal use but still act like a single network to the outside world. Each of such network parts is commonly referred to as a subnet that may further split over several subnets. Such a network appears to subscriber network devices as a single network; however, more than one local area network elements may exist over network connections such as Wide Area Network (“WAN”) connections, or optical network connections. Such networks typically include a plurality of subscriber nodes such as cable modems supporting home local area networks. A home local area network may include addresses assigned within a predetermined subnet administered, for example, by an Internet Service Provider, a cable operator such as a Multiple System Operator (“MSO”), or a Local Exchange Carrier (“LEC”), or agents thereof. In such a network, data flows may require network devices within the network to resolve network addresses of the devices that they want to communicate with. Often, the existing address resolution protocols cannot properly handle the address resolution for network devices on physically distributed subnets because of physical assumptions that are made by those protocols.
Typically, the address resolution is handled by an address resolution protocol (“ARP”). There are many versions of the address resolution protocol. One of the ARP versions includes a proxy address resolution protocol that allows other devices (a different device than the one queried) to respond to a query in place of network unreachable devices. The proxy address resolution protocol, similarly to other versions of the protocol, such as a directed address resolution protocol, or an inverse address resolution protocol, is widely used in such networks. However, these protocols have physical assumptions built into them. The physical assumptions include, for example, an assumption that the queried network device is unreachable by the normal address resolution protocol. However, as mentioned in the proceeding paragraphs, networks can have subnet splits over various disjoint nodes, and, for a proper operation of a network, it should not be assumed that a queried network device is, or is not, available. Further, in such networks, it should not be assumed that the correct response is that of a network device proxying the queried network device.
Thus, it is desirable to develop a method and system for resolving network addresses in physically and virtually distributed subnets, such as distributed Internet Protocol subnets.